<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>记住用户名</title>
    <style>
      #username {
        outline: none;
      }
    </style>
  </head>
  <body>
    <input type="text" id="username" />
    <input type="checkbox" id="remember" />
    <label for="remember">记住用户名</label>

    <script>
      var username = document.querySelector('#username');
      var remember = document.querySelector('#remember');

      if (localStorage.getItem('username')) {
        username.value = localStorage.getItem('username');
        remember.checked = true;
      }

      remember.addEventListener('change', function () {
        if (this.checked) {
          localStorage.setItem('username', username.value);
        } else {
          localStorage.removeItem('username');
        }
      });
    </script>
  </body>
</html>
